The proposed Research Plan will be integrated into and will further strengthen the research underlying the current Program Project grant (PPG) (PO1 AG21190), entitled Restless legs Syndrome: the Iron-Dopamine Connection. The Core Concept for this PPG, as stated in the "Introduction", is: "Restless Legs Syndrome symptoms result from altered dopaminergic mechanisms that are precipitated by a relative or absolute reduction of iron in the brain." An essential and integral component of the PPG Core Concept is "developing approaches using clinical, animal and laboratory studies to understand how iron is transported, stored and removed in the various brain regions". The primary brain region of interest in the PPG is the substantia nigra, located in the ventral midbrain (VMS). MRI and autopsy results demonstrate clearly reduced iron in the substantia nigra in those with Restless legs Syndrome. Core C of the PPG provides and maintains 30 BXD/Ty recombinant inbred strains of mice. Rl strains of rodents are derived from two initial parental strains of mice, in this case, C57BL/6J and DBA2/J. This panel was chose because the parental strains differ on a number of behavioral, neurobiological, immunological traits. Moreover, the DBA/2 parental strains differ in brain iron content, brain resistance to iron deficiency, dopamine function, and behaviors that are relevant to RLS. These BXD stains have natural phenotypic differences in their brain iron concentrations, i.e. there is a 3 fold differences in VMB iron found between those strains with the lowest and those with the highest iron concentration, despite normal peripheral iron levels. From these 32 strains, three strains with the highest and three strains with the lowest VMB iron concentration are being supplied for behavioral, neurochemical and histological analyses in Projects 3 and 4 of the PPG. The current Research Plan will use all 32 strains for quantitative genetic analysis of VMB iron content following dietary iron deficiency. In addition, we will study VMB gene expression response to iron deficiency in all 32 strains in iron-related genes that have been shown to operate in a network in the VMB under iron adequate diets. By associating VMB response in iron to changes in gene expression following induction of iron deficiency, we will identify those genes whose response predicts loss and/or retention of iron in this critical brain area for iron-dopamine interactions as they relate to RLS. We will then look for the genes that regulate expression of these iron-related protein genes. [unreadable] [unreadable] [unreadable]